1. Field of the Invention
This invention relates generally to the field of energy storage devices and, particularly, to a complete compact mobile flywheel system for storage and controlled release of kinetic energy.
2. Prior Art
The use of flywheels as energy storage devices is ancient art. The flywheel (FW) is an attractive means for storing energy for a number of reasons. In concept, it is a relatively simple device with which energy can be readily stored and extracted, either by mechanical means or by using electric motors and generators. In theory, the rate at which energy can be added or withdrawn is very high and there are no inherent limitations on the number of charge and discharge cycles that can be used. In these respects, mechanical energy storage offers marked advantages over the chemical energy storage of conventional batteries. Nevertheless, until relatively recently, it has generally been thought that flywheels do not offer a viable energy storage alternative. This has been largely due to the perceived disadvantages of flywheels relative to batteries with respect to cost and energy density. However, advances in materials technology and design of high speed rotating systems have made flywheels an increasingly attractive alternative. Moreover, environmental concerns relating to conventional energy storage means, particularly in the context of electrically powered vehicles, have focused renewed attention on flywheel systems. In recent years, there has been a great deal of interest in reducing the weight and size of flywheel based energy storage devices to provide such a device that can be practically utilized as a mechanical battery in an electrically powered vehicle. A total, non-hybrid FW system can be shown to have greater range and power than standard conventional internal combustion engine vehicles. This is possible with the advent of new materials and advanced electronics.
There are two basic flywheel configurations useful for high energy density mechanical batteries. One type has the flywheel fixed to the shaft and rotating together in unison. This configuration is sometimes referred to as a conventional rotor. The other type has the flywheel rotating about a stationary shaft. This is sometimes referred to as an inside out rotor. Both types of configurations have certain advantages and disadvantages. Advantages for the inside out rotor system include 1) compact volumetric packing, 2) no rotor to axle connection other than through the magnetic bearing, and 3) columnar support through stationary axle possible. Advantages for the conventional rotor system include 1) smaller and lighter magnetic bearings and motor/generator sub systems; 2) ability to remove heat from the motor/generator more easily precluding most heat dissipation into the composite rotor; 3) lower stresses on the magnetic bearing target actuators and lower stresses on the motor rotor; 4) reduced radial growth gap problems between the rotor and stator of the motor/generator and magnetic bearings; and 5) extension of the stator away from the permanent magnet rotating rotor, thereby totally removing magnetic drag losses during the quiescent (coasting) energy storage state. These losses can otherwise be high enough to almost fully discharge a FW by losses in 12 hours as compared to over a month by clever design of system components as described by this patent.